I totally agree. It was a one-on-one conversation between Dean and a grieving teenager who needed to hear that her father's death had meaning, so that's what Dean played up. She has no reason to care what the Winchesters did, so he left it out--especially since explaining it might well involve getting into a lot of horrific realities he doesn't need to drop on her in that moment. He didn't give any credit to himself in that scene either.

Also, at a Doylist level it would have been odd to have Dean go into an explanation of show history that the audience already knows, and that wasn't relevant to the episode.